1906 Proof $20
$20 Liberty Double Eagle gold coins are one of the world's most recognized gold pieces. Although $1, $2.5, $5 and $10 gold coins were already in circulation, the Mint realized that it could increase production of gold coins by minting a $20 gold coin, or double eagle, in half the time it took to produce two $10 gold coins with the same amount of gold. The mintage of the proof 1906 $20 was only 94 with a survival rate estimated at about half of that. This date is also tough in mint state making it just that more desirable in proof format.